Photosynthesis, Growth and Dry Biomass Production in Euglena gracilis Klebs as Affected by Three Growth Irradiance Levels

Aims: The research aimed to investigate the shade response of E. gracilis Klebs while making the irradiance a crucial factor for photosynthesis based physiological activities and its applicability for industrial level culture conditions.

Study Design: Euglena was cultured at three different light intensities of 30, 90, and 210 mol m-2s-1 photoautotrophically and axenically in modified Cramer-Meyer medium at 25 ˚C as batch cultures.

Methodology: The photosynthesis O2 evaluation of Euglena cultures was measured under exponential (EP), transitional (TP), and stationary phases (SP). The light compensation point (LCP), light saturation point (LSP), and dark respiration rate (DRR) were obtained. Cell volume and cell number in each culture were measured simultaneously. Cells were collected and obtained dry mass (DM) after drying aliquots at 80˚C. Specific growth rate (SGR) and relative growth rate (RGR) were calculated. Tests for homogeneity of variance were performed on all parameters and LSDs were used for the mean separation.

Results: In the TP, the lowest LCP was achieved in the higher light culture. The values of both the DRR and the LSP were the same as in EP. The DRR, LCP and LSP are lower in lower PFD cultures and decreased with increasing cell titers. The cellular growth levels were lower in lower light culture and decreased as each culture grew. Cellular DM was maintained constant in the EP, where SGR almost equaled RGR. In the EP, SGR was maintained constant in each culture, SGR displayed a saturation phenomenon. In the later TP, SGR became equal to RGR and all the cultures revealed constant DM.

Conclusion: Euglena photoautotrophic cultures can tolerate low light intensities. With the SGR and RGR behavior under the shade conditions, they can maintain the constant photosynthesis rate and constant dry matter level.